CA1265341A

CA1265341A - Nitro urea based blowing agents

Info

Publication number: CA1265341A
Application number: CA000493813A
Authority: CA
Inventors: Donald G. Rowland; Warren J. Peascoe; Byron A. Hunter
Original assignee: Uniroyal Chemical Co Inc
Current assignee: Uniroyal Chemical Co Inc
Priority date: 1984-12-05
Filing date: 1985-10-24
Publication date: 1990-02-06
Anticipated expiration: 2007-02-06
Also published as: IT8523035A0; DE3542919A1; DE3542919C2; JPS61148242A; IT1188208B; JPH038663B2; US4554294A

Abstract

ABSTRACT
The present invention relates to an improved nitro urea compound, specifically the zinc salt of nitro urea useful as a blowing agent composition, its preparation and its use.

Description

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NITRO UREA BASED BLOWING AGENTS
The present invention relates to an improved nitro urea compound useful as a blowing agent eomposition, its preparation and its use.
When making an extended material such as a foamed polymeric material, the polymeric material has conven-tionally been mixed with a blowing agent such as azodicarbonamide. The performance requirements of blowing agen~s have now become more and more cri~ical, and changes in the composi~ion of blowing agents can have significant effects on the end product. The instant invention provides a new compound consisting of a zinc salt of nitro urea which can be used as part of the blowing agent composition useful for the expanding of gas expandable polymers such as polyethylene, polyvinylchloride, and natural and synthetic rubbers.
The new compound is especially useful in the expansion of .
~ilicone elastomers.
The expanding of silicone rubbers, in the past, has been difficult to achieve with satisfactory results.
` Methods for preparing nitro urea are well known in !~
the prior art. United States Patent 2j311,784, tSpaeth) describes such a me~hod. HoweverJ there is no mentlon of a zinc salt of nitro urea.
25~ Reed - New Blowing Agents~for Foaming Plastics, ;:
British Plasticsj October, 1960, teaches the us~ of nitro urea as a blowing agent. However, no mention is made of the use of a zinc~salt of nitro urea.

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German Patent 1109876 teaches certain nitro urea derivatives useful as blowing agents. The zinc salt of nitro urea is neither mentioned nor suggested in this patent.
The compositions of this inventi.on find general use in foaming any gas expandable polymeric material, espe-cially those which are capable of setting to a normally solid state and having sufficient consistency and strength at the processing temperature (or to be enabled by virtue of the confining device) to retain the gas and preserve a cellular structure in the expanded product.
The processing temperature will depend upon a number of factors, including the nature of the polymeric material and its visco-elastic properties, upon the forming equipment being used and upon the nature of the end product desired. In general, for most effective results it is important that the polymeric material being expand- -ed has consistency and tensile strength sufficient to retain the individual micropores of gas a discrete cells, preventing coalescence to an undesirable coarse cell structure. This may generally be attained in the case o~
thermosetting resins by adjustment of the rate and state of cure to give the composition ~the deslred viscosity and s~rength at gas ~orming temperature. In the case of thermoplastic resins, the desired consistency and strength will generally ~e achieved by adjusting the temperature until the proper viscosity is obtained. The gas forming temperature wlll vary with the blowing agent , ~

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composition selected and will be selected depending on the polymer to be expanded.
The thermosetting polymer materials which may be used are any type of rubber which is curable or w lcanizable to a solid state, exemplified by natural rubber or synthetic rubbery polymers made from diolefins such as butadiene or isoprene, or ~heir copolymers with styrene, acrylonitrile, and the like; also, butyl rubber, polymerized halo-diolefins, such as neoprene, etc., as well as ethylene-propylene copolymers and ethyl-ene-propylene-non-conjugated diene terpolymer elastomers and silicone rubbers. Thermoplastic polymers suitable for being expanded with the blowing agents of this invention include polyethylene, polypropylene, polystyrenes, poly(vinyl chloride), polyamides, poly(styrene-acrylonitrile), polyacrylaee~ and the like.
~ The blowing agent compositions are mechanically ; mix d with the polymeric materials and, if desired, other customary adjuvants, fillersj plasticizers, stabilizers, etc., may also be added, prior to heating the mixture to temperatures at which decomposition of the blowing agent takes place. The amount of~the bIowing a~ent composition in the polymer may vary from 0.05 to~20Z, the quantity used depending upon the application and the density ; ~ 25 ~ ~ desired. Usually 0.1 to 15% concentrations o~ blowing ~ ~ :
agent~ suffice, and ordinarily 1.0 to 10% are~employed.
In accordance wlth the invention~, the new compound is prepared by a reaction of nitro urea with zinc oxide.

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Essentially stoichiome~ric amounts of zinc oxide and nitro urea area suspended in a suitable amount of water at room ~emperature. Stirring takes place for 30 min-utes-4 hours, and normally an exothermic reac~ion is observed. The reaction product is then filtered from a suspension, washed with water and dried. Alternatively, the zinc oxide and the nitro urea are compounded in a polymer which is used as a blowing agent composition.
In a urther embodiment of the invention, one may provide a mixture of azodicarbonamide with the aforesaid zinc salt of nitro urea or a mixture of nitro urea and zinc oxide. I~ has been found that the compound of the ins~ant invention serves as an activator when used in a blowing agent composition containing azodicarbonamide.
Blowing agent compositions using the novel compounds of the invention are described in the examples below.
The ollowing examples are illustrative as to specific embodiments of the invention without limiting its scope:

'' Preparation of zinc salt of nitro urea (a) Preparation of urea nitrate:
Into a 2000 ml 3-necked flask equipped with a mechanical stlrrer and a thermometer was introduced 1500 ml glacial a etic acid.
The stirrer was turned on, and 112.5 g of urea was added all at once. When all the urea had dissolved, 180 cc of concentrated nitric acid was gradually added ~- over a five minute period. Crystals formed almost , '' ` `~ , ' .~' ' .

~265:341 immediately. Application of a water bath kept the temperature under 25C. The mixture was allowed to stir overnight. The white crystalline product was filterPd on a sintered glass funnel under suction, and the resulting filter cake was washed with several separate portions of benzene (total of 300 ml). The product was dried in air at room temperature. The yield of 218.6 g represents 94%
of theory. The product melted a~ 159C.
(b~ Preparation of nitro urea:
Into a 3000 ml 3-necked flask equipped with a mechanical stirrer, heating mantle and a thermometer was introduced 2000 g (1905 ml) of glacial acetic acid and 200 g of acetic anhydride. The mixture was stirred and heated to 63C. The heating mantle was removed, and 2Q0 g o~ urea nitrate was added all at once. The temperature dropped to 58C, but remained steady at 57-58C as t~e mix was stirred for thirty minutes. During this period the solid suspensate gradually dissolved and finally formed a clear solution. Heat was momentarily applied (to 65C), and the heating mantle was removed. The mixture was allowed to stir and cool overnight. The mix was then cooled to 14C (ice water bath), and the crys-talline product was filtered on a si~tered glass funnel under suction. The product was washed with three 100 ml portions of benzene and then lOO ml of hexane. The , material was removed to a drying~paper and aIlowed to stand overnight. The yieId of 136.3 g (about 80~ of :
~ theory). mp: 144-145C.

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(c) Preparation of zinc salt of (b) .

To a 500 ml 3-necked, round bo~tom flask, equipped with a mechanical stirrer and a thermometer, were introduced 105 grams of nitro urea, 200 ml of water, and 40.7 grams ZnO at room temperature. The suspension was stirred for one hour; the temperature rose 24C ko 30C. The suspension was then filtered, and the precipi-tate was washed twice with cold waterO The mixture was dried overnight in an oven at 60C. The yield was 102 grams, and the decomposition ~emperature was determined to be 125C.

The zinc salt of ~xample 1 as well as mixtures with azodicarbonamide were evaluated as blowing agents. Table .15 1 below sets forth the decomposition point and the gas evolution measured in a gas burette (all in parts by weight).
TABLE I

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Decomposition Gas Evolution Run No. AZ ZSN Point (C) cc/g , __ ` 1 1.0 0 218 205 :: : 2 ~.9 0.1 122 ~61 ; ~ : 25 ~ 3 ~ ~.5 0~.5 : 124 ~ 180 :
4 ~ 0.35 0.~5 1~ 195 0 ~1.0 ~ 122 204 , _ _ _ __ _ _ ~ ' ' :
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REMARKS: AZ is azodicarbonamide. ZSN is the zinc salt of nitro urea of the instant invention (Run No. 1 is outside the invention) From these data it appear that as little as 10% of ZSN will lower the decomposition temperature of azodicarbonamide from over 200C to 122C.

. _ The rate of gas evolution may be accelerated by the addition of certain compositions of this invention as illustrated in Table II.
TABLE II

_ Nitro Urea, ZSN, ZnO, Gas Evolution Run No. AZ,g g g g cc/g Time to 90%
6 1.0 ~ --- ---- Nil ~---7 0 95 0~05 ~~~~ ---- 30 27 Min 8 0.95 ---- 0.05 ---- 193 14 Min 9 0.95 0.035---- 0.015 195 10 Min REMARKS: Experiments were conducted at 155C. It is apparent that not-~only in the decomposl~ion tempera-ture of azodicarbonamide reduced but also the gas evolu-tion is considerably accelerated.

Certain blowing agent compositions of this invention were evaluated for the expansion~of silicone rubber in the ~ollowing manner:
Blowing agent and curatives were added to the elastomer on a mill set for about 38C. Ater thorough .~
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, $ ~3 mixing, the compo~mded stock was sheeted off to a thick~
ness of 0.64 cm. Subsequently, the stock was press cured for 15 minutes at 150C and for 4 hours at 205C, after which t-ime the foamed silicone rubber was cooled at room temperature and tested. Recipes and results are dis-closed in Table III ~all in parts by we:ight):
TABLE III
Silicone Rubber 100 Curative - 1 1u2 Curative - 2 2.5 Nucleating Agent 3.0 ZSN 2.0 Density, lbs/ft3 54.2 Density, g/cm3 0.87 Density reduction, % 19 REMARKS: Curative - 1: 2,4 - dichlorobenzoyl peroxide; Curative - 2: dicumyl peroxide; Nucleating Agent: Diatomaceous earth The zinc salt of nitro urea (ZSN) was used for the expansion of polyethylene by first dry-blending low : density polyethylene with the blowing agent compositions : and then extending such blends by means of a Brabender :
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[trademark3~extruder at:25 RPM and through a circular exit die (temperature: 190C; diameter: 0.64 cm). The ~ ingredients and results are listed in Table IV.
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TABLE IV
Run No. 11 12 13_ _ Polyethylene 100 100 100 Azodicarbonamide --- 0.95 1.0 ~: ZSN 1.0 0.05 ---Foam density, g/cm30.765 0.558 0.785 :~ :
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Claims

WHAT IS CLAIMED IS:

1. A blowing agent composition selected from the group consisting of the zinc salt of nitro urea; a mixture of nitro urea and zinc oxide; a mixture of azodicarbonamide and the zinc salt of nitro urea;
and a mixture of azodicarbonamide, nitro urea and zinc oxide,

2. A gas expandable composition comprising a gas expandable polymer and an effective amount of the blowing agent composition of claim 1.

3. The composition of claim 2 wherein said polymer is elastomeric or thermoplastic.